WO2004026991A1

WO2004026991A1 - Liquid crystalline medium

Info

Publication number: WO2004026991A1
Application number: PCT/EP2003/008989
Authority: WO
Inventors: Michael Heckmeier; Eike Poetsch; Volker Reiffenrath
Original assignee: Merck Patent Gmbh
Priority date: 2002-08-20
Filing date: 2003-08-13
Publication date: 2004-04-01
Also published as: AU2003255437A1; DE10338111B4; DE10338111A1; WO2004026991A9

Abstract

The invention relates to a liquid crystalline medium containing at least one compound of formula (I), in which R1, R2, A1, Z1, (A), and m have the meanings indicated in claim 1, and electrooptical displays comprising such a liquid crystalline medium. The invention also relates to the compounds of formula (I).

Description

Liquid crystalline medium

The present invention relates to a liquid-crystalline medium, its use for electro-optical purposes and displays containing this medium.

Liquid crystals are mainly used as dielectrics in display devices, since the optical properties of such substances can be influenced by an applied voltage. Electro-optical devices based on liquid crystals are well known to the person skilled in the art and can be based on various effects. Such devices are for example cells with dynamic scattering, DAP cells (deformation of aligned phases), guest / host cells, TN cells with a twisted nematic ("twisted nematic") structure, STN cells ("super-twisted nematic"), SBE cells ("superbirefringence effect") and OMI cells ("optical mode interference"). The most common display devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.

The liquid crystal materials must have good chemical and thermal stability and good stability against electric fields and electromagnetic radiation. Furthermore, the liquid crystal materials should have a low viscosity and result in short response times, low threshold voltages and a high contrast in the cells.

Furthermore, they should be used at normal operating temperatures, i.e. possess a suitable mesophase in the broadest possible range below and above room temperature, for example a nematic or cholesteric mesophase for the above-mentioned cells. Since liquid crystals are generally used as mixtures of several components, it is important that the components are readily miscible with one another. Other properties, such as electrical conductivity, dielectric anisotropy and optical anisotropy, have to meet different requirements depending on the cell type and area of application.

BESTATIGUNGSKOPIE For example, materials for cells with a twisted nematic structure should have positive dielectric anisotropy and low electrical conductivity.

For example, media with large positive dielectric anisotropy, wide nematic phases, relatively low birefringence, very high resistivity, good UV and temperature stability and low vapor pressure are desired for matrix liquid crystal displays with integrated non-linear elements for switching individual pixels (MLC displays).

Such matrix liquid crystal displays are known. For example, active elements (i.e. transistors) can be used as non-linear elements for the individual switching of the individual pixels. One speaks then of an "active matrix", whereby one can distinguish two types:

1. MOS (Metal Oxide Semiconductor) or other diodes on silicon wafers as a substrate.

2. Thin film transistors (TFT) on a glass plate as a substrate.

The use of monocrystalline silicon as the substrate material limits the display size, since the module-like composition of various partial displays also leads to problems at the joints.

In the more promising type 2, which is preferred, the TN effect is usually used as the electro-optical effect. There are two technologies: TFTs made from compound semiconductors such as CdSe or TFT's based on polycrystalline or amorphous silicon. The latter technology is being worked on with great intensity worldwide.

The TFT matrix is applied to the inside of one glass plate of the display, while the other glass plate carries the transparent counter electrode on the inside. Compared to the size of the pixel The TFT electrode is very small and practically does not disturb the image. This technology can also be expanded for fully color-compatible image representations, with a mosaic of red, green and blue filters being arranged in such a way that one filter element each is opposite a switchable image element.

The TFT displays usually work as TN cells with crossed polarizers in transmission and are illuminated from behind.

The term MLC displays here includes any matrix display with integrated non-linear elements, i.e. In addition to the active matrix, displays with passive elements such as varistors or diodes (MIM = metal-insulator-metal).

MLC displays of this type are particularly suitable for TV applications (for example pocket TVs) or for high-information displays for computer applications (laptops) and in automobile or aircraft construction. In addition to problems with the angle dependence of the contrast and the switching times, difficulties arise with MLC displays due to insufficiently high specific resistance of the liquid crystal mixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K. , TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, Sept. 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, p. 141 ff, Paris; STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistors for Matrix Adressing of Television Liquid Crystal Displays, p. 145 ff, Paris]. With decreasing resistance, the contrast of an MLC display deteriorates and the problem of "after image elimination" can occur. Since the resistivity of the liquid crystal mixture generally decreases over the lifetime of an MLC display due to interaction with the inner surfaces of the display, a high (initial) resistance is very important in order to obtain acceptable service lives. In the case of low-voltage mixtures in particular, it has previously not been possible to achieve very high specific resistances. It is also important that the specific resistance increases as little as possible as the temperature rises as well as after temperature and / or UV exposure. The low-temperature properties of the mixtures from the prior art are also particularly disadvantageous. It is required that no crystallization and / or smectic phases occur even at low temperatures and that the temperature dependence of the viscosity is as low as possible. The state-of-the-art MFK displays therefore do not meet today's requirements.

In addition to liquid crystal displays which use background lighting, that is to say which are operated transmissively and possibly transflectively, reflective liquid crystal displays are also of particular interest. These reflective liquid crystal displays use ambient light to present information. This means that they consume significantly less energy than backlit liquid crystal displays with the appropriate size and resolution. Since the TN effect is characterized by a very good contrast, such reflective displays are still easy to read even in bright ambient conditions. This is already from simple reflective TN displays, as shown in e.g. B. wristwatches and calculators are known. However, the principle is also based on high-quality, higher-resolution active matrix displays such. B. TFT displays applicable. As with the common transmissive TFT-TN displays, the use of liquid crystals with low birefringence (Δn) is necessary in order to achieve a low optical delay (d • Δn). This slight optical delay leads to an usually acceptable low viewing angle dependence of the contrast (cf. DE 30 22 818). The use of liquid crystals with small birefringence is even more important in the case of reflective displays than in the case of transmissive displays, since the effective layer thickness * through which the light traverses is approximately twice as large as in the case of transmissive displays with the same layer thickness.

There is therefore still a great need for MLC displays with a very high specific resistance combined with a large working temperature range, short switching times even at low temperatures and low threshold voltage, which do not show these disadvantages or only show them to a lesser extent. With TN (Schadt-Helfrich) cells, media are desired that enable the following advantages in the cells:

extended nematic phase range (especially at low temperatures)

Switchability at extremely low temperatures (out-door use, automotive, avionics)

- increased resistance to UV radiation (longer life)

Small optical birefringence for thin layers

- low voltage

With the media available from the prior art, it is not possible to realize these advantages while maintaining the other parameters.

In the case of higher twisted cells (STN), media are desired which enable greater multiplexability and / or lower threshold voltages and / or wider nematic phase ranges (in particular at low temperatures). For this purpose, a further expansion of the available parameter space (clearing point, smectic-nematic transition or melting point, viscosity, dielectric parameters, elastic parameters) is urgently desired.

The object of the invention is to provide media, in particular for such MFK, TN or STN displays, which do not, or only to a lesser extent, have the above-mentioned disadvantages, and preferably at the same time have very high specific resistances and low threshold voltages. For this task, liquid-crystalline compounds are required which have a high clearing point and a low rotational viscosity. It has now been found that this object can be achieved if the liquid-crystalline compound of the formula I is used. The compounds of the formula I have a low rotational viscosity and bring about a significant improvement in the switching times in liquid-crystalline mixtures.

The invention thus relates to compounds of the formula I and a liquid-crystalline medium based on a mixture of polar compounds with positive or negative dielectric anisotropy containing one or more compounds of the formula I.

wherein

R is an unsubstituted, an alkyl or alkenyl radical which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen and has up to 15 C atoms, one or more CH ₂ groups in these radicals also being -O-, -S-, -C≡C-, -OC-O-, or -O-CO- can be replaced so that O atoms are not directly linked,

A ¹ a) a 1, 4-cyclohexenylene or 1, 4-cyclohexylene radical, in which one or two non-adjacent CH ₂ groups can be replaced by -O- or -S-,

b) a 1,4-phenylene radical in which one or two CH groups can be replaced by N, c) a radical from the group piperidine-1,4-diyl-,

1,4-bicyclo [2,2,2] octylene, a naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1, 2,3,4-tetrahydronaphthalene-2,6-diyl , Phenanthrene-2,7-diyl, fluorene-2,7-diyl,

where the radicals a), b) and c) can be substituted one or more times by halogen atoms,

Z ¹ -CO-O-, -O-CO-, -CF ₂ O-, -OCFr, -CH ₂ O-, -OCH ₂ -,

-CH ₂ CH ₂ -, - (CH ₂ ) -, -C ₂ F -, -CH ₂ CF ₂ -, -CF ₂ CH ₂ -, -CF = CF-, -CH = CH-, -C≡C - or a single bond,

R ² alkenyl with 2-7 C atoms and

m 0, 1 or 2

means.

The compounds of the formula I are colorless in the pure state and generally form liquid-crystalline mesophases in a temperature range which is conveniently located for electro-optical use. In particular, the compounds according to the invention are notable for their high clearing point and their low values for the rotational viscosity. They are stable chemically, thermally and against light.

In the mixtures according to the invention, the compounds of the formula I lead to a reduction in the switching times and low values for the rotational viscosity YL A> - preferably means in the compounds of the formula I.

H - or - () - o

n is preferably 0, furthermore 1.

If R ^{1 is} an alkyl radical and / or an alkoxy radical, this can be straight-chain or branched. It is preferably straight-chain, has 1, 2, 3, 4, 5, 6 or 7 carbon atoms and accordingly preferably means methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or Heptoxy, also methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy.

Oxaalkyl preferably means straight-chain 2-oxapropyl (= methoxymethyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R ^{1 is} an alkenyl radical, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it means especially vinyl, prop-1, or prop-2-enyi, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- or pent-4-enyl, hex -1-, 2-, 3-, 4- or

Hex-5-enyl, hept-1-, 2-, 3-, 4-, 5- or hept-6-enyl, oct-1-, 2-, 3-, 4-, 5-, 6- or oct -7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, dec-1-, 2-, 3-, 4-, 5- , 6-, 7-, 8- or Dec-9-enyI.

If R ^{1 is} an alkyl radical in which one CH ₂ group has been replaced by -O- and one has been replaced by -CO-, these are preferably adjacent. Thus, these include an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. These are preferably straight-chain and have 2 to 6 carbon atoms. Accordingly, they mean in particular acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-acetyloxyloxyl, propyl Methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxycarbonyl) ethyl, 3- (methoxycarbonyl) propyl, 3- ( Ethoxycarbonyl) propyl, 4- (methoxycarbonyl) butyl.

If R ^{1 is} an alkyl or alkenyl radical which is simply substituted by CN or CF ₃ , this radical is preferably straight-chain. The substitution by CN or CF ₃ is in any position.

If R ^{1 is} an alkyl or alkenyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain and halogen is preferably F or Cl. In the case of multiple substitution, halogen is preferably F. The resulting residues also include perfluorinated residues. In the case of single substitution, the fluorine or chlorine substituent can be in any position, but preferably in the ω position.

Compounds of the formula I with branched wing groups R ¹ can occasionally be of importance because of their better solubility in the customary liquid-crystalline base materials, but in particular as chiral dopants if they are optically active. Smectic compounds of this type are suitable as components for ferroelectric materials.

Compounds of the formula I with S _A phases are suitable, for example, for thermally addressed displays.

Branched groups of this type usually contain no more than one chain branch. Preferred branched radicals R ¹ are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methyl butyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl . 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy.

R ¹ preferably denotes straight-chain alkyl, vinyl, 1 E-alkenyl or

3-AlkenyI.

R ² preferably denotes CH ₂ = CH, CH ₃ -CH = CH, C ₃ H ₇ -CH = CH,

CH ₂ = CH-C ₂ H ₅ or CH ₃ -CH = CH-C ₂ H ₅ .

Preferred smaller groups of compounds of the formula I are those of the sub-formulas 11 to 18:

Particularly preferred media contain one or more compounds selected from the group of compounds of the formulas

The present invention also relates to the compounds of the formula I and their sub-formulas.

The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart) and under reaction conditions which are suitable for the implementations mentioned are known and suitable. Use can also be made of variants which are known per se and are not mentioned here in detail. The compounds of formula I can, for. B. can be produced as follows:

Scheme 1

Scheme 2

The invention also relates to electro-optical displays (in particular STN or MFK displays with two plane-parallel carrier plates which form a cell with a border, integrated non-linear elements for switching individual pixels on the carrier plates and a nematic liquid crystal mixture in the cell with a positive one dielectric anisotropy and high resistivity), which the like media contain and the use of these media for electro-optical purposes.

The liquid crystal mixtures according to the invention enable a significant expansion of the available parameter space.

The achievable combinations of clearing point, optical anisotropy, viscosity at low temperature, thermal and UV stability and dielectric anisotropy far exceed previous materials from the prior art.

The demand for a high clearing point, nematic phase at low temperature and a high Δε has so far only been met inadequately. Liquid crystal mixtures, such as. B. MLC-6476 and MLC-6625 (Merck KGaA, Darmstadt, Germany) have comparable

Clarification points and low-temperature stabilities, but they have relatively high Δn values as well as higher threshold voltages of approx.> 1.7 V.

Other mixing systems have comparable viscosities and values of Δε, but only have clearing points in the area of 60 ° C.

The liquid crystal mixtures according to the invention enable clearing points above 80 °, preferably above 90 °, particularly preferably above 100 ° C, while maintaining the nematic phase down to -20 ° C and preferably up to -30 ° C, particularly preferably up to -40 ° C, at the same time dielectric To achieve anisotropy values Δε> 4, preferably> 6, in particular> 7.0 and a high value for the specific resistance, as a result of which excellent STN and MFK displays can be achieved. In particular, the mixtures are characterized by small operating voltages. The TN thresholds are below 2.0 V, preferably below 1.8 V. It goes without saying that, by a suitable choice of the components of the mixtures according to the invention, higher clearing points (for example above 110 °) at higher threshold voltages or lower clearing points at lower threshold voltages can be achieved while maintaining the other advantageous properties. Likewise, with correspondingly little increased viscosities, mixtures with a larger Δε and thus lower thresholds can be obtained. The MFK displays according to the invention preferably operate in the first transmission minimum according to Gooch and Tarry [CH. Gooch and HA Tarry, Electron. Lett. 10, 2-4, 1974; CH. Gooch and HA Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975], where in addition to particularly favorable electro-optical properties such as low angle dependence of the contrast (DE-PS 30 22 818) with the same threshold voltage as in an analog display, a smaller dielectric anisotropy in the second minimum is sufficient. This allows using the invention

Mixtures in the first minimum achieve significantly higher resistivities than mixtures with cyan compounds. The person skilled in the art can set the birefringence required for a predefined layer thickness of the MLC display by means of simple routine methods by suitable selection of the individual components and their weight fractions.

The flow viscosity v ₂ o at 20 ° C. is preferably <60 mm ² • s ^" \ particularly preferably <50 mm ² • s ^{" 1} . The nematic phase range is preferably at least 90 °, in particular at least 100 °. This range preferably extends at least from -30 ° to + 80 °.

Capacity Holding Ratio (HR) Measurements [p. Matsumoto et al., Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); G. Weber et al., Liquid Crystals 5,

1381 (1989)] have shown that mixtures according to the invention containing compounds of the formula I have a significantly smaller decrease in HR with increasing temperature than analogous mixtures containing cyanophenylcyclohexanes instead of the compounds of the formula I. Formula R

•

_c The UV stability of the mixtures according to the invention is also considerably better, ie they show a significantly smaller decrease in HR under UV exposure.

The media according to the invention are preferably based on or. _n several (preferably one, further two, three or more) compounds of the formula I, ie the proportion of these compounds is 5-95%, preferably 10-60% and particularly preferably in the range of 15-40%.

The individual compounds of the formulas I to X and their sub-formulas which can be used in the media according to the invention are

15 either known, or they can be prepared analogously to the known compounds.

Preferred embodiments are given below:

20

The medium additionally contains one or more compounds selected from the group consisting of the general formulas II to X:

35

where the individual radicals have the following meanings:

Ro n-alkyl, alkoxy, oxaalkyl, fluoroalkyl, alkenyloxy or alkenyl, each with up to 12 carbon atoms

χo F, CI, halogenated alkyl, halogenated alkenyl, halogenated alkenyloxy or halogenated alkoxy, each with up to 8 C atoms,

-CH = CH-, -C ₂ H ₄ -, -CH2O-, -OCH2-, - (CH ₂ ) ₄ -, -C2F4-, -CF = CF-, -CF ₂ O-, -OCF ₂ - or -COO-,

Y ⁱ , Y ² , Y ³ and Y ⁴ each independently of one another H or F, and

r 0 or 1.

The compound of formula IV is preferred

F

.

or

In particular, the medium additionally contains one or more compounds of the formulas

and or

wherein R ° and Y ^{2 have} the meaning given above.

The medium preferably contains one, two or three, also four, homologs of the compounds selected from the group H1 to H18

(n = 1-12):

^C n ₂ n ₊ ι- H> - <O> - <O> - F H1

^C n ^H 2π ₊ 1- ^H > - <°> - (O> - F H2 _F

'rι 2n + 1 H O> - COO- O> - F H13

F

^C π ^H ₂ n ₊ r H> -CF, O- <O> - F H16

The medium additionally contains one or more dioxanes of the formula DI and / or DU,

wherein R ° has the meanings given in claim 4. R ° in the compounds of the formula DI and / or DU preferably denotes straight-chain alkyl or alkenyl having up to 8 carbon atoms.

The medium additionally contains one or more compounds selected from the group consisting of the general formulas XI to XVI:

where R) 0, X0,

Y3 and V4 each independently have one of the meanings given in claim 4, preferably X ° F, Cl, CF ₃ , OCF ₃ , OCHF ₂ . R ° preferably denotes alkyl, alkoxy, fluoroalkyl, alkenyl or alkenyloxy.

The proportion of compounds of the formulas I to X together in the total mixture is at least 50% by weight. The proportion of compounds of the formula I in the mixture as a whole is 5 to 50% by weight.

The proportion of compounds of the formulas II to X in the mixture as a whole is 30 to 70% by weight.

The medium contains compounds of the formulas II, III, IV, V, VI, VII, VIII, IX and / or X.

Ro is straight-chain alkyl or alkenyl with 2 to 8 carbon atoms.

The medium consists essentially of compounds of the formulas I to XVI.

The medium contains further compounds, preferably selected from the following group consisting of the general formulas XVII to XX:

XVIII

in which Ro and Xo have the meaning given above and the 1,4-phenylene rings can be substituted by CN, chlorine or fluorine. The 1,4-phenylene rings are preferably substituted one or more times by fluorine atoms.

The medium contains further compounds, preferably selected from the following group consisting of the formulas Rl to RXIV,

(O) alkyl * l

Alkenyl ^RiI1

Alkyl - H> - H> - (0 V-alkyr RVI II

Alkyl— <H> - (O) - (O) alkyl * RX

RXIll

embedded image in which

R ° n-alkyl, alkoxy, oxaalkyl, fluoroalkyl, alkenyloxy or alkenyl each having up to 8 carbon atoms,

d 0, 1 or 2,

Y H or F,

Alkyl or

Alkyl * in each case independently of one another, a straight-chain or branched alkyl radical each having up to 8 carbon atoms,

Alkenyl or alkenyl * each independently of one another is a straight-chain or branched alkenyl radical each having up to 8 carbon atoms

mean.

The medium preferably contains one or more compounds of the formulas

RIIa

Rllla

Rlllb

groove

0

C "HH ₉ - _{n + 1} ~ <HH>>-"<<HH> -CF, RIVa

V '2n + 1 \ ^π / \ / ³

where n and m each represent an integer from 2 to 8. 5

The weight ratio I: (II + III + IV + V + VI + VII + VIII + IX + X) is preferably 1:10 to 10: 1.

The medium consists essentially of compounds selected Q from the group consisting of the general formulas I to XVI.

It has been found that even a relatively small proportion of compounds of the formula I mixed with conventional liquid-crystal materials, but in particular with one or more compounds of formula II, ₅ III, IV, V, VI, VII, VIII, IX and / or X leads to a considerable lowering of the threshold voltage and to low values for the birefringence, at the same time broad nematic phases with low transition temperatures being observed smectically-nematically, which improves the storage stability. The compounds of the formulas I to X are Q colorless, stable and readily miscible with one another and with other liquid-crystal materials.

The term "alkyl" or "alkyl *" includes straight-chain and branched alkyl groups having 2 to 8 carbon atoms, in particular the ₅ straight-chain groups ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups with 2-5 carbon atoms are generally preferred. The term "alkenyl" or "alkenyl *" encompasses straight-chain and branched alkenyl groups having up to 8 carbon atoms, in particular the straight-chain groups. Particularly preferred alkenyl groups are C ₂ -C ₇ -1 E-alkenyl, C ₄ -C ₇ -3E-alkenyl, C ₅ -C ₇ -4-alkenyl, C ₆ -C ₇ -5-alkenyl and C ₇ -6- Alkenyl, in particular C -C ₇ -1E alkenyl, C ₄ -C ₇ -3E alkenyl and

C ₅ -C ₇ -4 alkenyl. Examples of preferred alkenyl groups are vinyl, 1 E-propenyl, 1 E-butenyl, 1 E-pentenyl, 1 E-hexenyl, 1 E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl , 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups of up to 5 carbon atoms are generally preferred.

The term "fluoroalkyl" preferably encompasses straight-chain groups with terminal fluorine, i.e. Fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorhexyl and 7-fluoroheptyl. However, other positions of the fluorine are not excluded.

The term "oxaalkyl" preferably includes straight-chain radicals of the formula C _n H ₂ n ₊ ι-O- (CH ₂ ) _m , in which n and m each independently represent 1 to 6. Preferably n = 1 and m is 1 to 6.

The response times, the threshold voltage, the steepness of the transmission characteristics, etc. can be modified in the desired manner by suitable choice of the meanings of Ro and X °. For example, 1 E-alkenyl residues, 3E-alkenyl residues, 2E-alkenyloxy residues and the like generally lead to shorter response times, improved nematic tendencies and a higher ratio of the elastic constants k ₃₃ (bend) and kn (splay) compared to alkyl or alkoxy. 4-alkenyl residues, 3-alkenyl residues and the like generally result in lower threshold voltages and larger values of k ₃₃ / kn in comparison to alkyl and alkoxy residues.

A group -CH ₂ CH ₂ - in Z generally leads to higher values of k ₃₃ / kn compared to a simple covalent bond. Higher values of k ₃₃ / kι. | enable, for example, flatter transmission characteristics in TN cells with 90 ° twist (to achieve gray tones) and steeper transmission characteristics in STN, SBE and OMI cells (higher multiplexability) and vice versa.

The optimal quantitative ratio of the compounds of the formulas I and II +

III + IV + V + VI + VII + VII + VIII + IX + X largely depends on the desired properties, on the choice of the components of the formulas I, II, III, IV, V, VI, VII, VIII, IX and / or X and on the choice of further components which may be present. Suitable proportions within the range given above can easily be determined from case to case.

The total amount of compounds of the formulas I to XVI in the mixtures according to the invention is not critical. The mixtures can therefore contain one or more further components in order to optimize various properties. However, the observed effect on the response times and the threshold voltage is generally greater the higher the total concentration of compounds of the formulas I to XVI.

In a particularly preferred embodiment, the media according to the invention contain compounds of the formulas II to X (preferably II and / or III), in which Xo OCF ₃ , OCHF ₂ , F, OCH = CF ₂₎ OCF = CF ₂ , OCF ₂ CHFCF ₃ , or OCF ₂ -CF ₂ H. A favorable synergistic effect with the compounds of formula I leads to particularly advantageous properties.

The mixtures according to the invention with low optical anisotropy (Δn <0.07) are particularly suitable for reflective displays. Low V _t h mixtures are particularly suitable for 2.5 V, 3.3 V drivers. 4V or 5V drivers are suitable for monitor mixes. Ester-free mixtures are preferred for the latter applications.

The construction of the MLC display according to the invention from Poiarisatoren, electrode base plates and ^{'surface-treated} electrodes corresponds to the conventional construction for displays of this type. Here is the The term “conventional construction” is broadly encompassed here and also includes all modifications and modifications of the MFK display, in particular also matrix display elements based on poly-Si TFT or MIM.

A significant difference between the displays according to the invention and those previously used on the basis of the twisted nematic cell, however, is the choice of the liquid crystal parameters of the liquid crystal layer.

The liquid crystal mixtures which can be used according to the invention are prepared in a manner which is conventional per se. As a rule, the desired amount of the components used in smaller amounts is dissolved in the components which make up the main constituent, advantageously at elevated temperature. It is also possible to use solutions of the components in an organic solvent, e.g. in acetone, chloroform or methanol to mix and the solvent after

To remove mixing again, for example by distillation.

The dielectrics can also further additives known to the person skilled in the art and described in the literature, e.g. B. contain antioxidants, stabilizers, UV filters, etc. For example, 0-15% pleochroic dyes or chiral dopants can be added.

C means a crystalline, S a smectic, S _c a smectic C, N a nematic and I the isotropic phase.

V-io denotes the voltage for 10% transmission (viewing direction perpendicular to the plate surface). t _on denotes the switch-on time and t _off the switch-off time for an operating voltage corresponding to twice the value of V ₀ . .DELTA.n. denotes the optical anisotropy and n ₀ the refractive index. Δε denotes the dielectric anisotropy (Δε = ε - ε _x , where εy is the dielectric constant parallel to the longitudinal axes of the molecule and ε _{x is} the dielectric constant perpendicular to it). The electro-optical data were measured in a TN cell at the 1st minimum (ie with a d • Δn value of 0.5 μm) at 20 ° C, unless expressly stated otherwise. The optical data were measured at 20 ° C, unless expressly stated otherwise. In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, the transformation into chemical formulas taking place according to Tables A and B below. All radicals C _n H _{2n +} ι and C _m H _{2m +} ι are straight-chain alkyl radicals with n or m C atoms. n and m each independently mean 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15. The coding according to Table B is self-evident. In Table A only the acronym for the body is given. In individual cases, a code for the substituents R1, R2, Li and L2 follows separately from the acronym for the basic body:

R2, Li, L2

nO.m OC _n H _2n + ι Cmrl2m + 1 HH n C _n H2n + 1 CN HH nN.FC _n H2n + 1 CN HF nF C _n H2n + 1 FHH nOF OC _n H _2n + ι FHH

nF.FF C _n H2n + ι FFF nCF ₃ C _n H2n + 1 CF ₃ HH

rEsN CrH2r + lO-C2H2s- CN HH nAm C _n H2n + 1 COOC _m H ₂ m ₊ ι HH nOCCF ₂ .FF _n H2n + 1 OCH ₂ CF ₂ HFF Preferred mixture components can be found in Tables A and B. Table A:

YP PYRP

BCH CBC

CCH CCP

CPTP

CEPTP

ECCP

CECP

PTP BECH

EBCH CPC

CGG CGU

CUP

CCQU

CWCQU

PUQU

Table B:

CBC NMF

PCH n Om

FET NCI

CP-nOCF ₃

CCH n Om

BCH n.FX

inm

CBC NMF

ECCP-nm

CCH-n1 EM

T-NFM

CGU-nF CCP-nOCF ₃ .F

CGG-n-F

CCP-nOCF _2- F (.F)

CCP nF.F.F

CGU-n-OXF

CUZU nF

CGU-n-O1DT

CCZU-n-F

CC-n-V1 CC-n-V

CCP-nOCF _a

BCH nF.F.F

CWCZU-n-F

CWCZG nF

CCOC-n-m

CGZU-n-F

CUZP-n-F

CGU-1V-F CCG-V-F

CGZP-n-F

UZP-n-N

CGZP-n-OT ^C n ^H 2n + 1 O V-COO- <O> -OCF ₃

CUZP-n-OT

CCQU-nF

Dec-U-n-F Nap-U-n-F

CWGZG-n-F

CWCZG-n-OT

CWCZP-n-OT

CWCQU nF

CCP nF.F

Table C:

Table C lists possible dopants which are generally added to the mixtures according to the invention.

C ₂ H

C 15 CB 15

CM 21

R / S-811

CM 44

CM 45

CM 47

R / S-1011

R / S 2011

R / S-3011

R / S-4011

Table D

Stabilizers that can be added, for example, to the mixtures according to the invention are mentioned below.

The following examples are intended to illustrate the invention without limiting it. Percentages above and below mean percentages by weight. All temperatures are given in degrees Celsius. Mp. Means melting point, Kp. Clearing point. Furthermore, K = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols represent the transition temperatures. Δn means optical anisotropy (589 nm, 20 ° C), the flow viscosity v ₂ o (mm2 / sec) was determined at 20 ° C. The rotational viscosity γi (mPa-s) was also determined at 20 ° C.

In the examples, "customary work-up" means: water is optionally added, extracted with dichloromethane, diethyl ether, methyl tert-butyl ether or toluene, separated, the organic phase is dried, evaporated and the product is purified by distillation under reduced pressure or crystallization and / or chromatography. The following abbreviations are used:

n-BuLi 1.6 molar solution of n-butyllithium in n-hexane

DMAP 4- (dimethylamino) pyridine

THF tetrahydrofuran

DCC N.N'-dicyclohexylcarbodiimide

LDA lithium dimethylamide

RT room temperature example 1

Step 1.1

A B

0.97 mol of A dissolved in 2.2 l of diethyl ether are mixed with 1.62 mol of zinc powder and 11.75 g of copper (II) acetate monohydrate. 1.45 mol of trichloroacetyl chloride is added dropwise within 0.5 h. Then allowed to stir for 48 h at room temperature. The reaction mixture is suctioned off from the zinc powder, diluted with 1 l of methyl tert-butyl ether, washed with water and concentrated. The residue is fritted over silica gel (toluene: n-heptane = 1: 1) and the eluate is concentrated.

Step 1.2

1.72 mol B dissolved in 3.6 I acetic acid are mixed with 6.336 mol zinc dust and stirred at 80 ° C. for 2.5 h. The mixture is allowed to cool to room temperature, the zinc salt is filtered off and the zinc salt is washed with methyl tert-butyl ether and concentrated. The residue is taken up in 2 l of methyl tert-butyl ether, washed with water and extracted with NaHCO ₃ solution. The organic phase is separated off and concentrated. The residue is fractionally distilled. Sp. 145 - 148 ° C at 14 mbar. Step 1.3

D

1.26 mol of C and 1.26 mol of methyltriphenylphosphonium bromide are suspended in 2.5 l of THF and at 10-20 ° C. 1.26 mol of potassium tert-butoxide are introduced in portions. The reaction mixture is stirred for 48 h at room temperature. After adding 1 l of water, it is acidified with HCl and mixed with 3 l of n-heptane. The organic phase is separated off and worked up as usual.

Step 1.4

1.01 mol D dissolved in 2.3 l of diethyl ether are mixed with 1.69 mol zinc powder and 12.3 g copper (II) acetate monohydrate. 1.52 mol of trichloroacetyl chloride are added dropwise within 0.5 h. The mixture is stirred overnight at room temperature. The zinc powder is then suctioned off, the eluate is diluted with 1 l of methyl tert-butyl ether and washed with water. The organic phase is worked up as usual.

Step 1.5

0.930 mol of E dissolved in 2 l of acetic acid are mixed with 3.43 mol of zinc dust with stirring. The reaction mixture is left at room temperature cool down, the precipitated zinc salt is suctioned off and washed with methyl tert-butyl ether. The organic phase is concentrated and worked up as usual.

Step 1.6

G

0.213 mol of F and 0.213 mol of methoxymethyl triphenylphosphonium chloride are suspended in 500 ml of THF and 0.213 mol of potassium tert-butoxide are added with cooling. The mixture is stirred overnight, stirred with sodium hydrogen chloride solution and diluted with 0.5 l of n-heptane. The organic phase is separated off and worked up as usual.

Step 1.7

H

0.12 mol G, 100 ml toluene, 30 ml H ₂ SO ₄ , 30 ml sulfuric acid and 0.72 g toluene-4-sulfonic acid monohydrate are boiled under reflux for 2.5 h. The reaction mixture is left to stir overnight and then worked up as usual.

Step 1.8

0.120 mol H and 0.120 mol methyltriphenylphosphonium bromide in 180 ml abs. THF suspended and mixed with 0.120 mol of potassium tert-butoxide at 5-20 ° C. After stirring for 12 hours overnight, water becomes admitted, with conc. Acidified HCI and diluted with petroleum ether 40 - 80 °. Finally, we are worked up as usual.

The following compounds of the formula become analogous

manufactured.

_P ^ - (A ¹ -Z ¹ ) _m

H

CH ₃

nC ₄ H ₉ nC _δ Hιι

CH ₂ = CH

CH ₃ CH = CH

R ¹ - (A ¹ -Z ¹ ) _π

H

CH ₃ - -

n

-C _δ Hi

- \ ^ -

CH ₂ = CH

-O.

CH; V_ _r

-O

C ₂ H ₅ ^ -o

CH ₂ = CHCH ₂ CH ₂ ^ o - ^/ - / ^" ^

CH ₃ CH = CHCH ₂ CH ₂ ^~ ^ - °

Examples mix

Example M1

CCP-2OCF3 7.0% clearing point [° CJ: +82.0

CCP-3OCF3 7.0% Δn [589 nm; 20 ° C]: 0.0772

CCP-4OCF3 4.0% Δε [1 kHz; 20 ° C]: 6.2

CCZU-2-F 4.0% γi [mPa ^■ s]: 80

CCZU-3-F 13.0% d ^■ Δn [μm]: 0.5

CCZU-5-F 2.0% twist [°]: 90

CGZP-2-OT 8.0% 10.0.20 [V]: 1.65

CGU-2-F 8.0%

CC-5-V 18.0%

CC-3-V1 10.0%

CCG-V-F 11.0%

C ₃ H ₇ H 8.0%

^

Example M2

CCP-2OCF3 7.0% clearing point [° C]: +80.5

CCP-3OCF3 7.0% Δn [589 nm; 20 ° C]: 0.0781

CCP-4OCF3 5.0% Δε [1 kHz; 20 ° C]: 6.3

CCZU-2-F 4.0% γi [mPa ^■ s]: 77

CCZU-3-F 14.0% d ^■ Δn [μm]: 0.5

CGZP-2-OT 9.0% twist [° j: 90

CGU-2-F 8.0% V-10.0.20 Y ^' - 1. 63

CC-5-V 15.0%

CC-3-V1 10.0%

PCH-302 2.0%

CCG-V-F 9.0%

C ₈ H ₇ - (ϊ ^ 10.0% Example M3

CCP-1 F.F.F 10.0% clearing point [° C]: +78.0

CCP-2F.F.F 8.0% Δn [589 nm; 20 ° C]: 0.0908

CCP-3F.F.F 9.0% Δε [1 kHz; 20 ° C]: 11.4

CCP-2OCF ₃ .F 12.0% γi [mPa ^■ s]: 120

CCP-2OCF3 8.0% d ^■ Δn [μm]: 0.5

CCP-3OCF3 8.0% twist [°]: 90

CCP-40CF ₃ 5.0%

CCP-50CF ₃ 7.0%

PUQU-2-F 6.0%

PUQU-3-F 9.5%

CGU-2-F 3.5%

CCGU-3-F 5.0%

CBC-33 2.0%

Example M4

CCP-2F.F.F 10.0% clearing point [° C]: +77.0

CCP-3F.F.F 12.0% Δn [589 nm; 20 ° C]: 0.0642

CCP-5F.F.F 4.0% Δε [1 kHz; 20 ° C]: 7.9

CCZU-2-F 4.0% γi [mPa ^■ s]: 140

CCZU-3-F 14.0% d ^■ Δn [μm]: 0.5

CCZU-5-F 4.0% twist [°]: 90

CCP-2OCF ₃ .F 7.0%

CCP-30CF ₃ .F 7.0%

CCP-5OCF ₃ .F 4.0%

CH-33 3.0%

CH-35 3.0%

CH-43 3.0%

CCH-3CF ₃ 10.0%

CCH-5CF ₃ 8.0%

C ₃ H ₇ H

^ 7.0% Example M5

CCP-2F.F.F 10.0% clearing point [° C]: +73.0

CCP-3F.F.F 12.0% Δn [589 nm; 20 ° C]: 0.0634

CCP-5F.F.F 4.0% Δε [1 kHz; 20 ° C]: 7.6

CCQU-2-F 4.0% γi [mPa ^■ s]: 128

CCQU-3-F 14.0% d ^■ Δn [μm]: 0.5

CCQU-5-F 4.0% twist [°]: 90

CCP-2OCF ₃ .F 7.0%

CCP-3OCF ₃ .F 7.0%

CCP-5OCF ₃ .F 4.0%

CH-33 3.0%

CH-35 3.0%

CH-43 3.0%

CCH-3CF ₃ 10.0%

CCH-5CF ₃ 8.0%

Example M6

CGZP-2-OT 9.0% clearing point [° C]: +66.0

CC-5-V 10.0% Δn [589 nm; 20 ° C]: 0.0848

CC-3-V1 13.0% Δε [1 kHz; 20 ° C]: 6.7

CCG-VF 4.0% γi [mPa ^■ s]: 67

CCP-2F.FF 10.0% d ^■ Δn [μm]: 0.5

BCH-3F.F.F 3.0% twist [°]: 90

CGU-2-F 6.0%

CCZU-2-F 3.0%

CCZU-3-F 7.0%

CCP-V-1 7.0%

PGU-2-F 9.0%

CCH-35 4.0%

CCH-3CF ₃ 3.0%

Example M7

CCP-1 F.F.F 2.0% clearing point [° C]: +76.0

CCP-2F.F.F 4.5% Δn [589 nm; 20 ° C]: 0.0767

CCP-2OCF3 5.0% Δε [1 kHz; 20 ° C]: 9.7

CCP-3OCF3 3.5% γi [mPa ^■ s]: 91

CCZU-2-F 4.0% d ^■ Δn [μm]: 0.5

CCZU-3-F 10.0% twist [°]: 90

CGZP-2-OT 8.0%

CGZP-3-OT 6.0%

CDU-2-F 8.5%

CDU-3-F 9.5%

CDU-5-F 7.0%

PGU-2-F 3.0%

CC-3-V1 11.0%

CCH-35 3.0%

C ₃ H ₇ - <H 15.0%

Claims

claims

1. Liquid-crystalline medium based on a mixture of polar compounds with positive or negative dielectric anisotropy, characterized in that it contains one or more compounds of the general formula I,

wherein

R ^{1 is} an unsubstituted, an alkyl or alkenyl radical which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen and has up to 15 C atoms, one or more CH ₂ groups in these radicals also being -O-, -S- , -C≡C-, -OC-O-, or -O-CO- can be replaced so that O atoms are not directly linked,

A ¹ a) a 1,4-cyclohexenylene or 1,4-cyclohexylene radical, in which one or two non-adjacent CH ₂ -

Groups can be replaced by -O- or -S-,

b) a 1,4-phenylene radical in which one or two CH groups can be replaced by N,

c) a radical from the group piperidine-1,4-diyl-, 1,4-bicyclo [2,2,2] -octylene-, a naphthalene-2,6-diyl,

Decahydronaphthalene-2,6-diyl, 1, 2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl, fluorene-2,7-diyl, where the radicals a), b) and c) can be substituted one or more times by halogen atoms,

Z ¹ -CO-O-, -O-CO-, -CF ₂ O-, -OCFj »-, -CH ₂ O-, -OCH ₂ -,

-CH2CH2-, - (CH ₂ ) ₄ -, -C2.F4-, -CH2CF2-, -CF2CH2-, -CF = CF-, -CH = CH-, -C≡C- or a single bond,

R ² alkenyl with 2-7 C atoms and

m 0, 1 or 2

means

contain.

2. Liquid-crystalline medium according to claim 1, characterized in that R ¹ in formula I.

CH ₂ = CH, CH ₃ CH = CH, C ₃ H ₇ -CH = CH, CH ₂ = CH-C ₂ H ₅ or CH ₃ CH ⁼ CH-C ₂ H ₅ ,

means.

Liquid-crystalline medium according to Claim 1 or 2, characterized in that it contains at least one compound from the group of the compounds of the formulas 11 to 18,

wherein

R ¹ and R ^{2 have} the meanings given in claim 1.

4. Liquid-crystalline medium according to one of claims 1 to 3, characterized in that it additionally has one or more

Compounds selected from the group consisting of the general formulas II, III, IV, V, VI, VII, VIII, IX and X contains:

- 65 -

5. Medium according to claim 4, characterized in that the proportion of compounds of the formulas I to X in the mixture as a whole is at least 50% by weight.

6. Medium according to one of claims 1 to 5, characterized in that it additionally contains one or more compounds of the formulas Rl to RXIV,

R ° - H> - <H X- (CF ₂ ) _d CF ₃ RIV

Alkyl— (H> - (H> -CH “O— <H V-alkyl * RVII

R VIII

- 66 -

AlkylM H> - H> -CH ₂ O - (H> - alkyl * RIX

Alkyl-M H> - O) - (O) alkyl * RX

RXIll

wherein

d 0, 1 or 2,

Y ¹ H or F,

Alkyl or

Alkyl * in each case independently of one another, a straight-chain or branched alkyl radical each having up to 8 carbon atoms, - 67 -

Alkenyl or

Alkenyl * each independently of one another a straight-chain or branched alkenyl radical, each with up to

8 carbon atoms

mean.

contains.

7. Medium according to claim 4, characterized in that X ° F, OCHF ₂ or OCF3 and Y ² H or F.

8. Use of the liquid-crystalline medium according to claim 1 for electro-optical purposes.

Electro-optical liquid crystal display comprising a liquid crystalline medium according to claim 1.

10. Compounds of formula I

wherein

R ^{1 is} an unsubstituted, an alkyl or alkenyl radical which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen and has up to 15 C atoms, one or more CH ₂ groups in these radicals also being -O-, -S- , -C≡C-, -OC-O-, or -O-CO- can be replaced so that O atoms are not directly linked, - 68

b) a 1,4-phenylene radical, in which one or two CH groups can be replaced by N,

c) a radical from the group piperidine-1,4-diyl-,

1, 4-Bicycio [2,2,2] octylene, a naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1, 2,3,4-tetrahydronaphthalene-2,6-diyl , Phenanthrene-2,7-diyl, fluorene-2,7-diyl,

-CO-O-, -O-CO-, -CF O-, -OCF2-, -CH2O-, -OCH2-,

-CH2CH2-, - (CH2) 4 ~, -C2F4-, -CH2CF2-, -CF2CH2-,

-CF = CF-, -CH = CH-, -C≡C- or a single bond,

R ^ alkenyl with 2-7 C atoms and

m 0, 1 or 2

wherein

mean. 69

11. compounds of the formulas 11 to 18,

wherein Ri and R2 have the meanings given in claim 10.